Process of producing heat treated powdered metal articles



Oct 1956 R. PETTIBONE ,768,917

PROCESS OF PRODUCING HEAT TREATED POWDERED METAL ARTICLES Filed Feb. 10, 1954 INVENTOR. ROB'RT' 1.. PETT/BQNE ATTORNEY PROCESS OF PRODUCING HEAT TREATED POWDERED METAL ARTICLES Robert L. Pettibone, Detroit, Mich., assignor to Eaton Manufacturing Company, Cleveland, Ohio, a corporation of Ohio Application February 10, 1954, Serial No. 409,502

1 Claim. (Cl. 14812.4)

This invention relates to powder metal articles and the metal analysis thereof.

Broadly the invention comprehends the provision of metal articles such as poppet valve spring retainers, rotator keys and caps for poppet valves and the like made from powder metal and being of an analysis providing the necessary physical qualities.

Although an extensive amount of powder metallurgical development has been carried on in the past few years, it is not believed that anyone heretofore has produced powder metal articles having a metal analysis as herein presented providing articles of economical construction and desired qualities of impact resistance, good tensile strength and good wear resistance.

Among the several objects of the invention is the provision of powder metal articles having a novel alloy analysis, that:

a. Are suitable for use in place of cast or stamped articles and have physical qualities at least equivalent, if not better than said stamped or cast articles;

b. Are much more economical to produce than cast and machined articles;

0. Include in the production thereof the steps of compacting iron powder to desired skeleton shape, sintering the skeleton, and infiltrating the sintered skeleton with an infiltrant such as copper or a copper alloy;

d. Include articles such as poppet valve spring retainers, rotator keys and the like;

e. Can be produced through specific powder metallurgy techniques to desired final shape and size;

f. Have high strength, good impact and good wear qualities; and,

g. Have a preferable analysis in the porous skeleton of 97 /2 commercial iron (Swedish iron), 1 /z% graphite and 1% sterotex, a lubricant for assisting in density gain in the cold pressing of the skeleton, infiltrated with copper or a copper alloy.

Other objects and advantages of the invention will appear from the following description taken in connection with the drawings forming a part of the specification, and in which:

Fig. l is a top elevation view of a valve rotator cap;

Fig. 2 is a cross-sectional view taken substantially along lines 22 of Fig. 1;

Fig. 3 is a top elevation view of a pair of valve rotator keys;

Fig. 4 is a cross-sectional view taken substantially along lines 4-4 of Fig. 3;

Fig. 5 is a bottom elevation view of a valve spring retainer; and,

Fig. 6 is a cross-sectional view taken substantially along lines 66 of Fig. 5.

The powder metal articles of this invention having a specific analysis providing for articles having high strength, good impact resistance and good wear qualities were devised as an economical substitution for machined cast or stamped articles. By so producing articles such as valve spring retainers, rotator caps and rotator keys nited States atent O 2,768,917 Patented 30, 1956 "ice 'by infiltration powder metallurgy methods, having a specific material analysis, a decided economical advantage as well as quality betterment was achieved over articles of this type produced by other means.

In the case of rotator keys, it was found that all previous parts produced by other means had to be chrome plated with hard chrome in order to have sufiicient wear resistance. Rotator keys made by infiltration powder metallurgy practice having a specific analysis as herein set forth, are far superior, without chrome plating, than the previously produced chrome plated rotator keys.

In the making of articles such as valve rotator keys 10, caps 12, for valve rotator mechanisms, and spring retainers 14, preferably commercially available iron base powder having a specific analysis by weight of 97 /2% commercial iron, 1%% graphite and 1% sterotex is compacted in steel dies to a density of approximately to the desired shape and size of the article to be produced. Sterotex is a commercial form of lubricant used to assist in the attainment of density in the cold pressing of the powder to porous skeleton form.

After compacting of the iron powder to porous skeleton form, the skeleton is sintered in a hydrogen atmosphere furnace at approximately 2050-2100" F. for approximately 30-60 minutes. The skeleton is next made solid by the infiltration of copper into the pores thereof. The copper for the purpose of carrying out the infiltration is used in powder form, compacted by cold pressing to desired shape which will permit its close fit to the skeleton whereby during infiltration the molten copper will be in direct contact with the skeleton, since the infiltration is solely dependent on capillary action. The infiltration is carried out in a furnace at a temperature of approximately 2050-2100 F. for approximately 30-60 minutes in a suitable reducing atmosphere such as hydrogen or vacuum. It is preferable for the purpose of producing a sound article to use an infiltrant consisting of by weight 80% copper, 10% iron and 10% manganese. The 10% iron is used to overcome the solubility of iron in the copper, and the 10% manganese is used to allow the easy removal of the excess infiltrant from the infiltrated skeleton after infiltration. The manganese is elfective since it has low wettability properties and will not adhere to the skeleton or infiltrated article. In some cases it is not necessary to sinter the skeleton before infiltration although it is recognized that the sintering cycle tends to provide for easier size control when close tolerances are required as well as give the carbon a greater chance to combine with the iron.

After infiltration the completed article is heat treated at approximately 1450 F. for between 4560 minutes. quenched in oil and subsequently stress relieved at 400 F. for 30-45 minutes. A hardness of between 45 and 50 Rockwell C is found to be suitable. The analysis of the article range-wise can be between 75 to by weight of iron powder and the balance copper, depending upon the density of the basic iron powder skeleton.

The carbon in the form of l /z% graphite, that is 1 /2% free carbon, becomes after heat treatment of the article .5 to .7% combined carbon with the iron and some small amount is dissolved in copper. The graphite in the skeleton can be varied between 1 and 1.5% by weight. Although the sterotex as used for lubricating purposes so as to attain density is preferable, it is not essentially necessary.

While this invention has been described in connection with certain specific embodiments, the principle involved is susceptible of numerous other applications that will readily occur to persons skilled in the art. The invention, therefore, is limited only as indicated by the scope of the appended claim.

2050-2l00 F. for approximately 30 60 minutes, heat 10 treating the infiltrated article at approximately 1450 F.

for between 45-60 minutes, next quenching the article in oil and subsequently stress relieving it at 400 F. for approximately 30-45 minutes producing an article which is 75 to 85 percent iron powder by Weight and the balance 5 copper.

References Cited in the file of this patent UNlTED STATES PATENTS 2,456,779 Goetzel Dec. 21- 1948 

